This patch eliminates the node pointer from struct of_device and the
of_node (or prom_node) pointer from struct dev_archdata since the node
pointer is now part of struct device proper when CONFIG_OF is set, and
all users of the old pointer locations have already been converted over
to use device->of_node.

Also remove dev_archdata_{get,set}_node() as it is no longer used by
anything.

Signed-off-by: Grant Likely <grant.likely@secretlab.ca>